Boron nitride (“BN”) is a thermally stable, highly refractory material of increasing commercial significance. Typically, boron nitride is produced by processes wherein boric acid is utilized as the boron source of reaction compositions. Suggested processes for producing boron nitride from boric acid are described in U.S. Pat. Nos. 2,922,699; 3,241,918; and 3,261,667 as well as in British Pat. Nos. 874,166; 874,165; and 1,241,206. U.S. Pat. No. 3,189,412 discloses a process to prepare boron nitride by passing nitrogen or ammonia or other nitrogen providing gas at 1200 to 1600° C. over a mixture comprising boric oxide, boric acid, or another boric oxide providing substance, carbon, and a catalyst, treating the reaction mixture with dilute mineral acid, and separating the boron nitride. JP Patent Publication No. 06-040713 discloses a process for producing boron nitride from colemanite, which is a hydrated calcium borate compound. It is thought that sodium compounds such as sodium borate can promote grain growth for BN particles in addition to the grain growth resulting from calcium borate compounds.
Applicants have discovered a process to use ulexite, a hydrated sodium calcium borate compound, in the direct manufacture of boron nitride instead of or in addition to boric acid as a reactant material. Using ulexite as a reactant in the boron nitride making process inherently enhances the grain growth of boron nitride, since ulexite contains sodium borate, providing an improved and economical process for making boron nitride of high purity and excellent yield.